One commonly cited factor is German militarism. Germany was the most powerful country in Europe in terms of military might, and it had been steadily increasing its military budget in the years leading up to the war. This increase in military power made other countries in Europe feel threatened, and it contributed to the general atmosphere of tension and fear that led up to the war.
Another factor often mentioned is German diplomacy. German diplomats were often seen as being aggressive and provocative in the way they dealt with other countries. This contributed to the growing distrust between Germany and its neighbours.
However, it is important to note that these are just two of many factors that contributed to World War I. Other factors include the rise of nationalism in Europe, the colonial rivalries between European powers, and the assassination of Archduke Franz Ferdinand of Austria in 1914.
In conclusion, there is no simple answer to the question of which country was responsible for World War I. It was a complex and multifaceted conflict that was caused by a variety of factors.